Fix a typo in C API documentation
Fix a typo in C API documentation

Summary:
Change "Certain nodes need *to* ability to measure themselves" to "Certain nodes need *the* ability to measure themselves".
Closes https://github.com/facebook/yoga/pull/430

Differential Revision: D4600091

Pulled By: emilsjolander

fbshipit-source-id: d20693b47291e79bd8c5f76e57d6dff2444333d2

facebook/yoga,yihuang/css-layout,yihuang/css-layout,facebook/yoga,facebook/css-layout,facebook/css-layout,yihuang/css-layout,yihuang/css-layout,facebook/css-layout,yihuang/css-layout,facebook/yoga,facebook/yoga,facebook/yoga,facebook/yoga,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/css-layout,facebook/yoga,facebook/yoga,yihuang/css-layout,facebook/css-layout,facebook/yoga,facebook/css-layout,yihuang/css-layout,facebook/css-layout,yihuang/css-layout,yihuang/css-layout,yihuang/css-layout